Dinitro-o-sec-butylphenol is a commercial herbicide. It can be made by reacting o-sec-butylphenol with concentrated sulfuric acid to form a sulfonated o-sec-butylphenol which can be reacted with aqueous sodium nitrate to form mainly 2,4-dinitro-6-sec-alkylphenol. This reaction sequence as applied to higher alkylphenols is described in U.S. Pat. No. 2,810,767. It is also known to use nitric acid in place of the aqueous sodium nitrate as the nitrating agent.
Although the above reaction sequence works well with highly purified colorless o-sec-butylphenol, it is not completely satisfactory with less pure o-sec-butylphenol which is slightly yellow to amber in color. With such impure o-sec-butylphenol starting material, the conversion to disulfonated o-sec-alkylphenol is incomplete, and the final product after the nitration is dark in color and contains a tar-like residue. Thus, a need exists to render impure o-sec-butylphenol satisfactory for sulfonation and nitration without an extensive purification procedure.